Electronic Structure and Superconductivity of Indium-Cadmium Alloys

Abstract

The superconducting transition temperatures (in zero magnetic field) of In-Cd alloys in the range 0-60 at.% cadmium have been measured. ${T}_{c}$ decreases from 3.406 to 3.245\ifmmode^\circ\else\textdegree\fi{}K in the tetragonal solid solution and from 3.55 to 3.00\ifmmode^\circ\else\textdegree\fi{}K in the cubic phase, with increasing Cd content. A kink in the ${T}_{c}$-versus-composition curve at 2 at.% Cd is attributed to Fermi-surface-Brillouin-zone interaction. This interpretation is supported by lattice-parameter determinations which show an anomaly at 2% Cd, and also by the magnetic susceptibility measurements of Verkin and Svechkarev. The existence of the superconductivity anomaly at $Z=2.98$ supports a recent hypothesis of Svechkarev concerning the electronic structure of indium. Measurement of reduced resistance ratio $\ensuremath{\rho}\ensuremath{\equiv}\frac{{{R}_{4.2}}^{\ensuremath{\circ}}}{({{R}_{273}}^{\ensuremath{\circ}}\ensuremath{-}{{R}_{4.2}}^{\ensuremath{\circ}})}$ show $\ensuremath{\rho}$ to be linear in Cd concentration $x$ up to the solubility limit at 5 at.% Cd, with a slope of 0.042/(at.% Cd). The data for the tetragonal phase are not linear on a plot of $\frac{\ensuremath{\Delta}{T}_{c}}{x}$ versus $\mathrm{ln}x$, and thus do not fit the present theory of ${T}_{c}$ variation in primary solid solutions. At the tetragonal-cubic phase transition, ${T}_{c}$ jumps by 10% without change of electron/atom ratio, cell volume, or ionic mass. The superconductivity data are all consistent with the published phase diagram of Heumann and Predel.